Open AccessAges, metallicities and [α/Fe] ratios of globular clusters in NGC 147, 185 and 205
Author(s) -
Sharina M. E.,
Afanasiev V. L.,
Puzia T. H.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10925.x
Subject(s) - physics , globular cluster , astrophysics , metallicity , stellar population , astronomy , galaxy , hubble sequence , milky way , balmer series , hubble space telescope , horizontal branch , population , spiral galaxy , spectral line , star formation , emission spectrum , medicine , environmental health
We present measurements of ages, metallicities and [α/Fe] ratios for 16 globular clusters (GCs) in NGC 147, 185 and 205 and of the central regions of the diffuse galaxy light in NGC 185 and 205. Our results are based on spectra obtained with the SCORPIO multislit spectrograph at the 6‐m telescope of the Russian Academy of Sciences. We include in our analysis high‐quality Hubble Space Telescope /WFPC2 photometry of individual stars in the studied GCs to investigate the influence of their horizontal branch (HB) morphology on the spectroscopic analysis. All our sample GCs appear to be old ( T > 8 Gyr) and metal‐poor ([Z/H]≲−1.1) , except for the GCs Hubble V in NGC 205 ( T = 1.2 ± 0.6 Gyr, [Z/H]=−0.6 ± 0.2) , Hubble VI in NGC 205 ( T = 4 ± 2 Gyr, [Z/H]=−0.8 ± 0.2) and FJJVII in NGC 185 ( T = 7 ± 3 Gyr, [Z/H]=−0.8 ± 0.2) . The majority of our GCs sample has solar [α/Fe] enhancement in contrast to the halo population of GCs in M31 and the Milky Way. The HB morphologies for our sample GCs follow the same behaviour with metallicity as younger halo Galactic GCs. We show that it is unlikely that they bias our spectroscopic age estimates based on Balmer absorption‐line indices. Spectroscopic ages and metallicities of the central regions in NGC 205 and 185 coincide with those obtained from colour–magnitude diagrams. The central field stellar populations in these galaxies have approximately the same age as their most central GCs (Hubble V in NGC 205 and FJJIII in NGC 185), but are more metal‐rich than the central GCs.